Because of the low cost, simple structure, low power consumption and small size, the light emitting diode (LED) is applied in display and illumination technologies.
For general LED fabrication, an LED epitaxy structure is formed on a substrate directly, while a cathode electrode and an anode electrode are respectively fabricated on different sides of the substrate. This conventional structure has a better current spreading efficiency, but an increased LED package area is necessary. Therefore, a flip-chip LED has been gradually developed over the last few years.
The p-type semiconductor layer and the n-type semiconductor layer of the flip-chip LED are exposed on the same side of the LED epitaxy structure in the flip-chip LED fabrication to allow the anode electrode and the cathode electrode to be on the same side of the LED, and the LED epitaxy structure with electrodes can thus be flipped onto a solder directly by flip-chip packaging technology. Thus, conventional wire bonding for the package is not necessary, and a smaller package size and higher device reliability are obtained.
However, the light emitted upward from the flip-chip LED is absorbed by the substrate and cannot pass through the substrate for complete outward output. Therefore, although the flip-chip LED is beneficial for device package, the flip-chip LED suffers a lowered LED light output intensity.
Further, the field of LED technology is highly focused on the development of LED with higher brightness. Unfortunately, only the light emitted upward from the LED counts as light output; the light emitted downward is partially absorbed by the material below the LED and cannot be another source for light output. More particularly, the light emitted downward from the flip-chip LED is easily blocked and scattered by electrodes. Thus, the light output of the LED only depends on the luminance properties of the LED itself, and the light output intensity is limited in improvement.